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mercury deposition
from precipitation
volcanic eruptions
release mercury
natural volatilization
and runoff from rocks
and minerals
dry deposition of
particulate mercury
mercury
volatilization and
runoff from gold
and mercury mines
mercury
mines
n
a
t
u
r
a
l
industrial
discharge
into
aquatic
systems
burning of
fossil fuels
releases mercury
coal electric plant
factory
crop burning and
forest fires release
mercury to
atmosphere
mercury pathway
to humans is
fish consumption
mercury
bioaccumulation
in fish
mercury in water and
sediment reaches fish
sediments
mercury evaporation
from lakes and rivers
mercury
evaporation
from oceans
domestic
sewage
mercury
vapor
possible seepage
in ground water
landfill
mercury
vapor
Mines use toxic chemicals
including cyanide, mercury, and
sulphuric acid, to separate metal from ore. The chemicals used
in the processing are generally recycled, however residues may
remain in the tailings, which in developing countries are often
dumped directly into lakes or rivers with devastating conse-
quences. The accidental spillage of processing chemicals can
also have a serious impact on the environment. For example, at
The Acid Mine Drainage (AMD)
is the number one environmental problem facing the
mining industry. AMD occurs when sulphide-bearing minerals in rock are exposed
to air and water, changing the sulphide to sulphuric acid. It can devastate aquatic
habitats, is difficult to treat with existing technology, and once started, can continue
for centuries (Roman mine sites in Great Britain continue to generate acid drainage
2 000 years after mining ceased). Acid mine drainage can develop at several points
throughout the mining process: in underground workings, open pit mine faces, waste
rock dumps, tailings deposits, and ore stockpiles. (Miningwatch).
Artisanal small-scale gold mining of placer deposits
occurs mostly in developing
countries. Examples include Brazil, Venezuela, Colombia, Guyana, Suriname, Philip-
pines and New Guinea. Between 10 and 15 million people worldwide produce 500
to 800 tonnes of gold per year, in the process emitting as much as 800-1000 tonnes
of mercury. Gold recovery is performed by removing sediments from the river and
adjacent areas and feeding them through a number of mercury-coated sieves. The
mercury amalgamates with the gold in the sediments, separating the gold from the
rest of the material. The gold-mercury amalgam is then heated. The heat drives off
the mercury, leaving the gold product. While most of the mercury condenses and is
recovered, some is emitted to the air and is eventually deposited on nearby land or
water surfaces. Mercury deposited on land ultimately reaches streams and rivers
through runoff. Roughly 1 kilogram of mercury enters the environment for every kilo-
gram of gold produced by artisans. (United States Geological Survey).
the Baia Mare mine in Romania cyanide is used to extract gold
from slurry. In January 2000 a dam containing tens of thou-
sands of tonnes of slurry burst, poisoning the local river with
cyanide and heavy metals. Up to 100 tonnes of cyanide were
released into the river, a tributary of the Danube. The drink-
ing water supply for more than 2 million people was affected.
Within hours, dead fish were seen washed up along the river.
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After Mining
Filtering soils
Groundwater
Surface runoff
Mine
Sulfide
OXYGEN + WATER + SULPHIDE = SULFURIC ACID
Heavy Metals Fish Mortality
Filtering soils
Groundwater
Rainfall filtering
through soil
Surface runoff
Before Mining
Sulfide
Extraction decreases groundwater depth and
natural filtration, and increases the
groundwater contamination.